1. Technical Field
The present invention relates to the field of electromechanical motion amplifiers having an active module of electroexpansive material, such as piezoelectric material. Two pistons are utilized, with force transmission means, preferably in the form of an elastomer, for effecting an amplified movement of the second piston in response to movements of the first piston.
2. Background Art
Several devices utilizing motion amplifiers having a pair of differential-area pistons separated by a hydraulic medium and driven by a piezoelectric stack are known to the prior art. In all instances where both pistons move along the same axis, they move in the same direction, and in one particular instance, the hydraulic medium is specifically identified as comprising mercury. In all the other arrangements with which I am familiar, the hydraulic medium is generically identified as "hydraulic fluid." None of the prior art devices to which I have reference discusses the need for, nor discloses, a highly advantageous temperature compensating mechanism.
The instant invention distinguishes over the relevant prior art teachings in three key respects. First, by the preferred use of an elastomer as the hydraulic medium. Second, by its inclusion of a temperature compensating mechanism, and third, by its ingenious structural arrangement wherein the two pistons move along the same axis, but in opposite directions. These distinguishing features appear to be particularly significant.
By comparison with my highly advantageous device, U.S. Pat. No. 3,501,099 to Benson discloses an electromechanical actuator which comprises a stack of piezoelectric material 12 which, when electrically excited, pushes a piston 18 forward into a chamber 20. Chamber 20 is filled with a fluid which is forced against valve body 26 when piston 18 pushed down, due to the expansion of the stack of piezoelectric material. As disclosed in column 2, line 68 to column 3, line 5, since the area of piston 18 is much greater than that of the exposed area of valve body 26, motion amplification to a degree that is proportional to the ratio of the surface areas is obtained. In addition to the FIG. 1 embodiment, Benson further shows additional embodiments which likewise use the expansion of a stack of piezoelectric material for urging against a large diameter piston, which in turn effects a motion amplification by a smaller diameter piston through a non-compressible fluid.
U.S. Pat. No. 3,877,226 to Blum discloses the use of both large and small diameter pistons for translating an abrupt linear motion of a cylinder into a longer duration, more uniform linear motion, with the movement of the small diameter pistons being amplified. In contrast to the present invention, there is no mention of using a stack of piezoelectric crystals as the urging force. Nor, for that matter, is there any mention of the use of an elastomer as the moving member.
U.S. Pat. No. 4,318,023 to O'Neill discloses an amplified piezoelectric actuator which does not use any elastomer for transferring the movement of one piston to the next.
U.S. Pat. No. 3,598,506 to O'Neill discloses the use of a stack of piezoelectric crystals for actuating a piston by means of a fluid. In contrast to the present invention, only one piston is disclosed in O'Neill.
In addition, the use of piezoelectric crystals for translational movement is well known, as witnessed by U.S. Pat. No. 3,551,764 to Evans wherein an electrically-powered actuator using a pair of piezoelectric elements is disclosed. Further showing a piezoelectric actuator is U.S. Pat. No. 4,471,256 to Igashira et al, wherein a stack of piezoelectric elements are used.
In summation, although the Benson patent shows the use of a stack of piezoelectric material, as well as large and small diameter pistons in order to accomplish motion amplification, it is quite clear that the novel and highly advantageous structural configuration shown in the present invention differs substantially and significantly from the embodiments shown by Benson.